Fault detection, e.g. locating faults such as breaks, shorts, discontinuities, degraded components, and improperly terminated transmission lines, is a task performed by CATV service providers in order to pinpoint problems in the cable distribution network. Faults within the distribution network are typically characterized by an impedance mismatch, i.e. the impedance of the fault is different from the characteristic impedance of the transmission lines of the distribution network. For example, transmission lines in a CATV distribution subsystem typically have an impedance of approximately 75 ohms; however, a short on the transmission line would have an approximately zero impedance and a break would have an approximately infinite impedance.
One problem with faults in the distribution subsystem is that faults, due to their impedance mismatch characteristics, reflect signals transmitted through the distribution network. As a result, faults in the distribution network may also cause problems throughout the distribution network due to interference from reflected signals. Therefore, it is important for CATV service providers to be able to easily identify and locate faults within the network in order to cure reception problems of a single subscriber and to remove fault generated interference from the distribution network as a whole.
Frequency domain reflectometry utilizes a reflectometer that applies a sweep signal to a distributed communication network. The sweep signal is an RF signal that is swept from an initial frequency to a final frequency, e.g. 5 MHz to 82 MHz, in relatively small increments, e.g. 0.075 MHz. If an impedance mismatch exists within the network the impedance mismatch will reflect each transmitted signal back to the reflectometer at the same frequency as the transmitted signal, but retarded in phase. As a result of this reflection, a standing wave is generated. The reflectometer measures the level of the standing wave at each swept frequency in order to obtain a reflected sweep response signal. The retardation of the reflected sweep response signal is such that the minimums of the reflected wave will align to ½ the wavelength of the impedance mismatch from the reflectometer. Due to this known relationship, the reflectometer may determine the distance from the reflectometer to the impedance mismatch.
In order to fully characterize a home network for its ability to support triple play services and home networking standards such as Multimedia over Coax Alliance (MoCA) it is necessary to measure the frequency response from any node in the home network to any other node from 5 to 1500 MHz. Test instruments available today, which would allow a single technician to perform these tests, consist of a transmitting device and a separate receiving device (e.g., JDSU LST-1700). Characterization of a home network using such instruments is time consuming; therefore, there is a need to provide a more convenient and cost effective tool for home network characterization.
As Multiple System Operators (MSOs) and Telcos continue to add high bandwidth advanced services to their systems such as digital video, DOCSIS cable modems, switched digital video (SDV), and MoCA, the performance of coax and twisted-pair home network wiring becomes more critical. Given that most home network wiring was installed before the current bandwidth requirements were established, the performance of many home networks is marginal. This results in higher operator expense when installing and servicing triple-play services due to the increased technician troubleshooting time and cost of replacing entire home networks. In order to reduce these expenses, installers and service technicians need a tool that can fully map, troubleshoot, and qualify a home wiring network at the push of a button.
Accordingly, it is an object of this invention to provide a method of home network characterization and a system implementing this method which overcome the deficiencies of conventional network characterization systems and methods.